The present invention relates to a texture mapping appartus for projecting picture element information in a desired area on a texture plane, on figure data in a desired area on a display plane.
There has been increased the demand for ensuring designing or image effects by projecting a desired area of figure data previously supplied from an image input device, or figure data drawn by a figure drawing device, on a surface of a desired solid figure. To satisfy such demand, there have been provided texture mapping apparatus for projecting and displaying a desired two-dimensional figure on a desired three-dimensional figure.
There is known a texture mapping apparatus in which a two-dimensional texture original figure is divided in line segments in the scan line direction, and the line segments thus obtained are subjected to an inverse perspective transformation for each picture element while the line segments are being scanned on the display plane in the scan line direction, see ("What is the Texture Mapping (1)", in the Collection of Lectures and Theses [III] by Takeshi SHIBAMOTO and Makoto KOBAYASHI, Association of Data Processing, Published in Sep. 9, 1985).
In the texture mapping apparatus arranged as abovementioned, it is required to carry out a matrix operation for each picture element, creating a problem of slow processing speed. Further, accurate mapping cannot be always achieved dependent on the combination of unit polygons constituting a texture original figure with unit polygons constituting a figure on the display plane. This disadvantageously presents deterioration in quality of figure data displayed on the display plane.
Further, there are instances where polygons constituting a figure on the display plane present a butterfly plane. It is therefore required to previously judge whether or not three apexes of a polygon exist on the same plane on which another apex exists, thereby to identify whether or not the polygon presents a butterfly plane. This not only results in time-consuming further processing, but also presents the problem that accurate texture mapping cannot be achieved.
More specifically, when the apexes of opposite sides of a polygon exist on a spline curved line, a butterfly plane is inevitably generated by dividing the polygon in unit polygons in the form of a quadrilateral. When this butterfly plane is divided into two triangles and these triangles are filled to achieve texture mapping, portions of the polygon which should not be filled, are consequently filled in view of the nature of the butterfly plane.